1. Field of the Invention
The present invention relates generally to a wireless communication method, and more specifically, to a communication method for transmitting frames by adapting priority in a wireless personal area network (WPAN) based on IEEE 802.15.3 standard.
2. Description of the Related Art
Wireless personal area network (WPAN) enables bidirectional communications amongst devices such as computers, peripherals, mobile terminals, or home appliances within a short distance of 10 m by connecting the devices through wireless networks, and supports various applications. In contrast to local area network (LAN) or wide area network (WAN), the WPAN is one of personal wireless communication networks, not conventional infrastructured networks, to thus implement small, inexpensive, and power efficient solutions. The WPAN may be applied to applications such as, for example, home networks.
Currently, IEEE 802.15.3 Task Group (TG) is developing the WPAN standard. The IEEE 802.15.3 enables high data rate transmission of 11 to 55 Mbps with lower power, and a data transmission range is limited to 10 m. The IEEE 802.15.3, which is in process of standardization by IEEE 802.15.3a TG which specifies WPAN systems using a ultra-wide band system, is to provide a physical layer enhancement to 100 Mbps and aims at applications such as multimedia transmission of wireless videos over a short distant connectivity like home networks.
A unit of the WPAN is a piconet which configures networks, including a piconet coordinator (PNC) and more than one mobile device (DEV) sharing a unique network identifier. The PNC forms a piconet by transmitting beacons, provides a basic communication timing, and provides wireless communication services such as the quality of service (QoS), power save modes, and media access control (MAC).
According to the IEEE 802.15.3 specification, the piconet is formed without pre-planning and for only as long as the piconet is needed. A plurality of DEVs of a piconet respectively and independently share a single medium in a peer-to-peer manner, and communicate with each other in a multihop manner, in which this type of the piconet is also referred to as an ad hoc network.
The multihop manner transmits data packets from a source node to a destination node via the plurality of the DEVs which perform as both a host and a router, in the communications between DEVs over the ad hoc networks. Since the piconet covers at most 10 m, the data packets may not be transmitted directly from the source node to the destination.
Since the DEVs of the piconet communicate by sharing the single medium, communications of each DEV should be allowed with proper timing allocations by controlling access to the medium of each DEV to thus prevent collisions in the DEVs communications.
FIG. 1 is a diagram illustrating an example of the conventional WPAN. Referring to FIG. 1, the WPAN includes a plurality of DEVs 100 to 140. One of the DEVs is a coordinator 100 which broadcasts beacon frames to synchronize the DEVs 110, 120, 130, and 140 of the network. The DEVs 100 to 140 synchronized by the beacons, communicate with each other in the peer-to-peer manner according to the timing based on a superframe within the network.
FIG. 2 is a diagram illustrating a structure of a superframe for the wireless communications in the WPAN according to the IEEE 802.15.3 standard.
Referring to FIG. 2, the superframe includes a beacon period, a contention access period (CAP), and a channel time allocation period (CTAP). A length of the CAP is determined by the PNC and is sent to each DEV during the beacon period.
During the beacon period, information for managing the communications over the entire piconet is transmitted. For example, a sync signal is transmitted for synchronization of each DEV of the WPAN, and the time slot allocation (CTA) is set to each channel.
During the CAP, each DEV contendingly communicates using carrier sense multiple access with collision avoidance (CSMA/CA), and an asynchronous data frame and a command frame are transmitted. The command frame conveys control information such as a request and a response of the communication, a channel time request (CTR), and other control signals.
The CTAP includes a plurality of CTAs and management CTAs (MCTAs), which are exclusively allocated to each channel by the PNC for transmitting data frames, and uses a time division multiple access (TDMA) method. The MCTA is a type of CTA and is used for communications between the PNC and the DEV. Accordingly, if a data rate of PHY is enhanced, high rate transmission of data frames is feasible.
However, a clear channel assessment (CCA) time, a waiting time, and a backoff time for the CSMA/CA of the CAP have fixed values and require a high rate of relative overhead for the frame transmission. Thus, the high rate as in the CTAP is not expected.
The data frame and the command frame are transmitted in equivalent contention during the CAP, to thus considerably delay the transmission of the control information which is a pre-stage of the data transmission for establishing a communication channel. As a result, the delay of the control information degrades high data rate transmission.